Effects of drawing strain and post-annealing conditions on microstructural evolution and tensile properties of medium- and high-carbon steels

Variation in the microstructure and tensile properties with the warm drawing strain and subsequent annealing of 0.45 wt% C (45C) medium-carbon steel and 0.82 wt% C (82C) high-carbon steel was investigated. The morphology and size of ferrite and pearlite changed considerably with applied strain during drawing and with annealing temperature and time, which made the tensile properties of the drawn steels vary considerably. With increasing drawing strain to ~2.5, the yield strength increased significantly from 393 to 1332 MPa for the 45C steel and from 673 to 1876 MPa for the 82C steel; this was attributed mainly to the strain hardening caused by severely deformed ferrite and/or enhanced particle hardening caused by cementite segmentation. During annealing of heavily drawn steels, ferrite grain growth and coarsening of broken cementite particles occurred simultaneously, which caused effective recovery of the ductility of severely drawn steels. These results demonstrate that the tensile strength and elongation of medium- and high-carbon steel wires can be tuned considerably by controlling the extents of drawing and annealing, thereby widening their applicability and facilitating their manufacture to match their mechanical properties to each application.